In recent years, research has been advancing on optical tomographic image generating devices (hereinafter referred to as “OCT: Optical Coherence Tomographs”) which visualize the depth structure of the inside of a biological body by making use of an interference effect of light.
In particular, recently, optical tomographic image generating devices for fundus oculi have emerged, in which three-dimensional images of the inside of a retina can be observed, and they have manifested their power in the diagnosis of illness with risks of vision loss.
Conventionally, in one of such optical tomographic image generating devices for fundus oculi, a low coherence interferometer has been used. As for such optical coherence eye-fundus tomography device, a time domain optical coherence eye-fundus tomography device (Time-Domain OCT, hereinafter referred to as “TD-OCT”) is known, such device visualizing the depth structure of the inside of a biological body based on an interference signal in a depth direction of an object, which is obtained by mechanically manipulating a reference light path length.
Such TD-OCT has a low coherence light source with a wide wavelength width, and a light beam from such light source is divided into two beams and one of them is delivered to an object (i.e. an eye ball).
The TD-OCT causes the beam for scanning the object (hereinafter referred to as an “object-scanning light beam” or “probe light beam”) to scan in a depth direction and to interfere with the beam for reference (hereinafter referred to as a “reference light beam”), which is the other of the divided beams. The TD-OCT then detects the position of diffusion in the object based on the interference fringes generated due to such interference.
Additionally, the TD-OCT causes the object-scanning light beam delivered to the object to scan in a direction lateral to a light path or causes the object to move in a direction lateral to such light path so that a cross sectional image of the object can be obtained (see, for example, Non-Patent Document 1).
On the other hand, a spectrum domain OCT (Fourier Domain OCT, hereinafter referred to as “FD-OCT”) is known, such FD-OCT carrying out interference of light waves in a Fourier space (spectrum domain), instead of carrying out the same in the real space (time domain), without making use of such mechanical scanning in the depth direction. The FD-OCT has a measuring speed which is several tens of that of the TD-OCT.
In particular, the FD-OCT drives a galvanometer mirror to scan a retina forming plane and obtains a three-dimensional tomography image. Thus, since the FD-OCT can obtain a three-dimensional tomography image only with two-dimensional mechanical scanning, a rapid tomographic measurement can be performed (see, for example, Non-Patent Document 1).
On the other hand, in the FD-OCT, since no high-order aberration in a Zernike approximate polynomial is present, and by making use of a light beam only with low-order aberration (i.e. the object-scanning light beam), a component for correcting the high-order aberration is unnecessary, and thus, the number of components can be reduced. In addition, as to such FD-OCT, an FD-OCT which can maintain a high resolution for the images of a retina and a high operability of the device has emerged (see, for example, Patent Document 1).
Moreover, in an adaptively-controlled optics system (AO), a method is commonly known in which a movement distance of a retina is estimated by calculating mutual correlation between two images (see, for example, Non-Patent Document 2).